Field
The present disclosure relates to a backlight module using a multi junction technology (MJT) light emitting diode (LED) and a backlight unit including the same. More particularly, the present disclosure relates to a backlight module which employs an MJT LED configured to increase an effective light emitting area of each of light emitting cells to allow operation at low current, and a backlight unit including the same.
Description of the Background
A liquid crystal display creates an image by controlling transmittance of a backlight light source. Although a cold cathode fluorescent lamp (CCFL) has generally been used as a backlight light source in the related art, light emitting diodes (hereinafter, LEDs) are being recently used due to various advantages such as low power consumption, long lifespan, eco-friendliness, and the like.
Backlight units can be classified into edge type backlight units and direct type backlight units according to the locations of LEDs for backlighting a liquid crystal display. In an edge type backlight unit, with LEDs arranged as light sources on a side surface of a light guide plate, light entering the light guide plate from the light sources is used for backlighting of a liquid crystal panel. Thus, the edge type backlight unit can reduce the number of LEDs and does not require strict control of quality deviation among the LEDs, thereby enabling manufacture of low power consumption products, which is advantageous in terms of cost. However, in the edge type backlight unit it is difficult to overcome contrast between a corner area and a central area of the liquid crystal display and it is difficult to create high quality images.
Alternatively, a direct type backlight unit is placed under a liquid crystal panel and allows light emitted from a surface light source, which has substantially the same area as that of the liquid crystal panel, to directly illuminate a front side of the liquid crystal panel. The direct type backlight unit can overcome contrast difference between a corner area and a central area of the liquid crystal display and can achieve high quality images.
However, in the direct type backlight unit, if each of the LEDs does not illuminate a relatively wide area for backlighting, a number of LEDs must be densely arranged, thereby causing increase in power consumption. Moreover, deviation in quality between the LEDs can make it difficult to secure a uniform screen illumination due to uneven backlighting of a liquid crystal panel.
Particularly, with the increasing size of liquid crystal panels, the size of the direct type backlight unit is also increased, thereby causing deterioration in stability or reliability of the direct type backlight unit. Specifically, since the LED backlight unit controls the operating current supplied to a plurality of LED groups, that is, LED arrays, through a plurality of LED drive circuits, the number of LED drive circuits and the number of LED corresponding arrays are significantly increased as the size of the LED backlight unit increases. As a result, a disconnection can occur between the plurality of LEDs or LED arrays arranged adjacent each other, whereby the drive circuits are damaged due to overcurrent, overvoltage, or overheating, thereby deteriorating the stability and reliability of the backlight unit.
FIG. 1 is a configuration block diagram of a typical backlight unit using LEDs in the related art. With reference to FIG. 1, problems of the related art will be described in more detail. As shown in FIG. 1, a typical backlight unit 1 includes a backlight control module 2 and a backlight module 5.
The backlight control module 2 includes an operating power generator 3, which generates/outputs DC power based on input voltage Vin input from an external power source, and an operation controller 4 controlling operation of each of a plurality of LED arrays 6a˜6n constituting the backlight module 5. The operating power generator 3 generally generates DC voltages such as 12V, 24V, 48V, and the like as operating power.
The backlight module 5 includes a plurality of LED arrays 6a˜6n each formed by connecting a plurality of LEDs in series, and an optical unit (not shown) for enhancing efficacy of light emitted from the plurality of LED arrays 6a˜6n. In FIG. 1, the backlight unit 5 includes n LED arrays 6a˜6n connected to each other in parallel and each including five LEDs connected to each other in series. Here, since each of the LEDs used in the backlight unit generally has a forward voltage level in the range from 3V to 6.5V and is difficult to individually control/operate when connected to the operating power generator 3, plural LEDs are connected to each other in series to constitute LED arrays such that each of the LED arrays can be operated/controlled. In such a typical backlight unit 1 in the related art, the operation controller 4 is configured to control brightness of all of the LED arrays 6a˜6n constituting the backlight module 5 through pulse width modulation (PWM) control with respect to the operating power supplied to the backlight module 5 in response to an external dimming signal (Dim). Otherwise, in such a typical backlight unit 1, the operation controller 4 adjusts the operating current flowing through a specific LED array among the n LED arrays 6a˜6n in response to an external dimming signal (Dim) to control brightness of the specific LED array.
LEDs used in such a typical backlight unit 1 are generally single-cell LEDs capable of being operated at low voltage and high current. For example, such a single-cell LED has an operating voltage of 3.6V and can be operated at an operating current of 250˜500 mA. Thus, in order to control operation of the backlight module 5 constituted by such single-cell LEDs, peripheral circuits including the operation controller 4 in the related art must be constituted by large capacity electronic devices capable of handling large current, thereby causing increase in manufacturing costs of the backlight unit 1. In addition, the peripheral circuits including the operation controller 4 are damaged due to the high current operation characteristics of the aforementioned typical single-cell LEDs, thereby causing deterioration in stability or reliability of the backlight unit 1. In addition, the high current operation characteristics of the single-cell LEDs cause an increase in power consumption and a droop phenomenon.